The bullhead Cottus gobio L. is the only freshwater cottid found in the UK. The Cottidae (sculpins) are mostly marine fish, with around 300 species worldwide. A small species, the bullhead exceptionally reaches 15 cm in length and a weight of 28g. It is easily identified by its large head (which can account for 25% of body length) with eyes on the top and a dorso-ventrally flattened tapering body adapted to life on the bottom of flowing waters.
The bullhead is widely distributed throughout Europe. It occurs from Greenland and Scandinavia in the north to Italy in the south. In the British Isles it is common in England and Wales, excluding northwest Wales. The bullhead is also absent from Ireland and present in only three catchments in Scotland: the Clyde, Forth and Don.
Despite its wide distribution, the bullhead can only be considered indigenous to east-flowing, and some south-flowing, English rivers, corresponding to the connection with mainland Europe before the end of the last Ice Age 10,000 years ago. Explanations for its current distribution include natural headwater capture and human introduction. The latter is likely to be linked to the fact that bullheads were once caught for food and for use as live-bait for larger fish species.
One important issue that must be taken
into account when undertaking condition assessment, is that bullheads
have very limited home ranges, and genetically discrete populations exist
in small sections of rivers or in individual tributaries. Consequently,
several distinct populations of bullheads may exist within each SAC river
catchment, and these do not genetically mix. This has serious implications
for the conservation status of bullheads in SAC rivers, as the stock in
each river cannot necessarily be treated as one population that freely
mixes.
Ecology of the Bullhead, Cottus gobio
